Men should land on Mars before the century’s end. Some optimists say this could happen by the late 1970s but others argue that the formidable problems to be solved make any time period less than some 30-odd years unrealistic. Unless, they add, there is a now unforeseen breakthrough in launching giant loads into orbit or propelling such loads through interplanetary space. Even before man lands on Mars, however, the question of whether some form of life exists there will be answered ... next ye...